Electrode for the recovery of metals from solutions by electrolysis.



No. 883,170. PATENTED MAR. 31, 1908. S. B. CHRISTY. ELECTRODE FOR THERECOVERY OF METALS FROM SOLUTIONS BY ELEGTROLYSIS.

urmonxon FILED MAB-.10, 1906.

2 SKEETS-SHEET 1.

CL. C.

I a! R m 0 W2, Nflw ./Z. 4/ w. W 6 a F 0 E 6 We NW No. 883,170. PATENTEDMAR. 31, 1908. S. B. CHRISTY.

ELECTRODE FOR THE RECOVERY OF METALS FROM SOLUTIONS BY ELEGTROLYSIS.

APPLICATION FILED MAR. 10, 1906.

2 SHEETS-SHEET 2.

'fornia, have invented certain new UNITED STATES PATENT OFFICE.

SAMUEL B. OHRISTY, OF BERKELEY, CALIFORNIA.

ELECTRODE FOR THE RECOVERY OF METALS FROM SOLUTIONS BY ELECTROLYSIS.

Specification of Letters Patent.

Patented March 81, 1908.

Application filed inch 10, 1906 Serial No. 806,247.

To all whom it may concern:

Be it known that I, SAMUEL B. Omus'rr, a citizen of the United States,residing at Berkeley, in the county of Alameda, State of Caliand usefulImproved Electrodes for the Recovery of Metals from Solutions byElectrolysis; and .I do hereby declare the following to be a full,

clear, and exact description of the same.

vMy inventionrelates to electrodes used for the recovery, byelectrochemical means, from the dilute solutions that result from theextraction of ores of gold, silver, copper,

zinc, lead, nickel, cobalt, and-other metals;

but articularly gold, silver, and copper; whet er these solutions beacid'or alkaline; and whether the metals be combined as chlorids,sulfates, bromids, cyanids, or other soluble salts.

My invention consists in novel forms and constructions of theseelectrodes, in order to adapt them to the most rapid and e'conom-' icalmethods of removing the metallic content from such solutions. The termelectrode here used covers both the anode, by which the positivecurrentof electricity enters the solution, and the cathode, ,by which itleaves the solution.

Referring to the accompanying drawings Figure 1 is a verticallongitudinal section through a deposition box containing simple perviousanodes and cathodes. Fig. 2 is a vertical cross section through thesame. Fig. 3 is a vertical section through a number of simple perviousanodes and. cathodes showing the active and inactive portions of simplepervious. cathodes. Fi 4 is a vertical section through a deposition boxcontaining a compound pervious electrode, showing how a portion of thesame acts as an anode, another portion as a cathode. and how theinterior portion is inactive. Fig. 5 is avertical section through asimple pervious anode, and through compound pervious electrodes, and,finally, through a simple pervious cathode. Fig. 6 is a verticallongitudinal section through a deposition box, showing how the same isbest arranged to utilize the advan-' tages of compound perviouselectrodes. Fig. 7 is a vertical section through simple erviouselectrodes and compound pervious e ectrodes constructed to resistcorrosive action of the electrolyte on the anode side of the compoundpervious electrodes. Fig. 8 is a vertical elevation of a box arranged tocontain the material used in a compound perform of deposition box viouselectrode. Fig. 9 is a vertical section through a simple pervious anode,a com-- pound pervious electrode, and a simple pervious cathode. Fig. 10is a top view of the same. Fig. 11' is a vertical sectional elevation ofan improved form of a simple pervious anode composed of lead wirescoated with roxid of lead, stretched upon a suitable 'rame. Fig. 12. isa vertical section through the same.

The difficulties of recovering metals from such dilute solutions asoccur in the extraction of ores is very much greater than, and of anentirely different nature from those which occur in ordinaryelectroplating of articles with gold, silver, copper, and other metals.In the latter case one has to do with concentrated solutions ofapproximately constant' composition; while in the recovery of metalsfrom solutions obtained from the extraction of ores, it is necessary totreat solutions which are constantly being depleted of their'metalliccontent, thus becoming oorer conductors; and to remove, substantla ly,all of the metals contained'in such solutions. This is a roblem of thegreatest diflicult In order that the metal shall be complete y removedin a reasonable time, it is necessary to have numerous cathode surfacesof enormous area, and a similar number of anodes but preferably, whenossible, of smaller area; and the best resu ts are obtained bycirculating the solution in such a manner that it is brought intointimate contact with anodes and cathodes in rapid alternation so as tomaintain a constant supply of metal at the cathode for the electriccurrent to precipitate, as has been fully ex lained in my U. S. Patent,No. 756,328, (ated April 5, 1904. In order to get effectiveprecipitation, it is necessaryto have a large number of pervious anodesand cathodes throu h which the solution may circulate. T e

referred in said atent is .herem shown in Figs. 1 and 2, w ich are hererepeated for the sake of a better understanding of my present invention.In these figures, B is the deposition box. The solution to be treatedenters the deposition box in Fig. 1 at A, circulates, as shown by thearrows, through the pervious anodes a and pervious cathodes c and passesout at Z.

. The iervious anodes a are made of some insolub e electric conductingsubstance; and the ervlous cathodes c are made of some perviouselectro-conductmg substance of sufficiently reat surface area. Theformof cathode shown in Figs. 1 and 2, marked 0, I shall call in thefollowing specifications, siniple pervious cathodes; and the anodesmarked a I-shall call simple pervious anodes. The electrodes shown inFigs. 1 and 2 have given excellent results in the recipitation of metalsfrom their solutions, ut they have the great disadvantage of requiringan enormous number of electrical connect1ons-one being required for eachanode, and one for each cathode. -As a consequence, whenever an anode orcathode is to be removed, a cer tain amount of trouble is created inestablishing and securing the electrical connections and constantwatchfulness is necessary to maintain good electrical contacts.

In Fig. 3 are shown two such pervious cathodes marked 0, which maybesupposed to be made of wire cloth, or fragments of coke or graphitecontained in a suitable box with sides of cheese-cloth, and lacedbetween pervious anodes a. It wou d, ordinarily, be supposed that thewhole of the inner surface of said pervious cathodes would be effectivefor precipitating metal upon it. v I have, however, found that such isnot the case. The metal is precipitated by the electric current on suchpervious cathodes only to a moderate depth. This depth de ends on thepermeability of the material use and increases with its perviousness, orthe free interstitial space. When granules of graphite, or of coke,about one-eighth of an inch in diameter, are placed in such frames, themetal is deposited for a depth of about 1 to 3 granules, according tothe perviousness. With wire cloth it penetrates to a greater depth, butin all cases if the thickness of said pervious electrode exceeds acertain amount, as shown in Fig. 3, the interior portion of the cathode(marked 0) is practically with no deposit upon it; while the outerportions (marked with a minus sign) become coated with-metal. Theinterior portion (marked 0) may be said to be in an electrolytic shadow,and consequently to receive from the electric current practicall nometal upon it. Here, and in what fo ows in these specificationsregarding this neutral portion' 0 pervious electrodes I refer only tothe metal deposited by the electric current and not to the metaldeposited by the chemical action of the material of the electrodeitself, u on the solution as sometimes happens. e depth through'whichthe current will enetrate and act on the solution varies rom one-eighthto one-half an inch with ordinary degrees of perviousness. N ow, themore compact the particles of the electric conducting substance, theless deep will the metallic deposit penetrate the cathode, untilfinally, when the perviousness diminishes to that of a sheet of compactmetal, the metallic deposit does not penetrate the cathode end of the atall, but is all deposited on the exterior surface of said solid cathode.Now the discovery of this fact, which at first sight appears to be aserious disadvantage in the use of pervious cathodes, has led me todevise a simplification in the ervious electrodes used for depositingmetal s. To illustrate this I refer to Fig. 4.

Fig. 4 shows a deposition box B'which is to containa solution of somemetal such as copper sulfate, or cyanid of gold or silver and potassium.At a is shown an insoluble anode of carbon or platinum, and at c acathode of carbon or platinum. Now if there be placed in the solutionbetween these anodes and cathodes by which the current electrode madeeither of sheets of wire cloth,

or a mass of granules of coke or graphite contained in a suitablepervious vessel, and a positive electric current caused to enter thesolution at the anode a, and to pass outof the solution by the cathodec, the end of the pervious electrode a nearest the anode a becomescharged with negative electricity, as indicated by the minus sign, andcopper or gold and silver will be deposited upon that ervious electrodefor a distance of from one-eighth to one-half an inch or more, dependingupon the perviousness. The opposite side, indicated by the plus sign, ofthe pervious electrode (marked (1 becomes charged with ositiveelectricity for a similar distance bac from its face. The intermediateportion of the pervious electrode (marked 0) is neither negatively norpositively'electrified, and practically no metal will be deposited thereby the electric current. My first im rovement consists in utilizing thisidea in t e construction of what I here designate as a compound perviouselectrode, one face of which acts as an anode, and the other face ofwhich acts as a cathode, and between which there exists a portion actingneither as a cathode nor an anode, but sim ply conducting electricityjust as a solid metallic conductor would do. Fig. 5 shows the manner inwhich said compound pervious electrodes are used. The deposition box isnot shown in this figure, but only the electrodes. The compound perviouselectrodes are marked E and E They may be of any number desired. Thepositive electric current enters the solution by means of a sim lepervious anode E", the whole of which ecomes charged with positiveelectricity. -At a suitable distance, preferably as small as possiblewithout short-circuiting, is placed the compound pervious electrodemarked E. Y

The side 0 nearest the anode E acts as a cathode and is marked with aminus sign. The middle portion bis neutral and is marked 0. The otherside 0. acts as an anode and is marked with a plus sign. At a suitabledistance is placed a second compound pervious electrode E and as manymore as may be necessary, and finally a simple pervious cathode E andalso marked with a minus si n through which the electric current leavest e solution. The manner in which I prefer to arrange such a combinationof compound pervious electrodes is shown in. Fig. 6: At

is shown a large tank or reservoir containing the solution to betreated. sition box. The solution is forced to circulate through saiddeposition box B by means of a centrifugal pump P, driven by a motor M,or'other suitable means, from the tank T through the deposition box B,and back again through pi e p, repeatedly. It is also possible to circuate the solution from the tank through, the box once only, provided thebox is made sufficiently long to secure complete preci itation, in asingle passage; but the metho here shown in Fig. 6

is much preferable, and I prefer to use it, or

its e uivalent. At D is shown a shunt woun dynamoor other source ofelectricitygiving a direct current. From D the ositive electric currentflows to the sim l e pervious anode E". It thus enters the ox, passesthrough the solution to compound pervious electrode E, then through thesolution again to compound pervious electrode E etc. until it finallyreaches the simple pervious cathode E, b which it leaves the box, andreturns tlirough the ammeter A to the negative pole of the dynamo D. AtV is shown a suitable voltmeter for determining the voltage between theterminals of the deposition box B. In using these compound perviouselectrodes, Fig. 5 shows what takes place. Each of the compound perviouselectrodes E, E etc., receives a metallic deposit only upon the side 0which is'negatively electrified. The side a receives no metallic depositand the portions 1) practically none, unless by the chemical action ofthe electrode itself. The portions marked a being an anode, are liabletabs attacked by the solution unless made'of some substance insoluble inthe electrolyte, such as platinum or gra hiteparticularly that graphitemade in t e electric furnacebut in some solutions, as in alkalinesolutions containing no chlorids or sulfates. iron may be used for thisurpose; but this form of construction prec udes the use of solublemetals such as copper, zinc, etc., on the anode side of perviouselectrode. In order to make it possible to utilize such metals or otheroxidizable electro-conducting substances as a material for use on thecathode side of compoundpervious electrodes, I have devised the form ofcompound pervious electrodes shown in Fig. 7. E shows a simple perviousanode which introduces the ositive current into the solution. E and 2show a new form of compound pervious electrodes, and E shows a compoundpervious electrode which is used B is the depoa which acts as an anodeis made of some suitable substance which is at once an electricalconductor and is insoluble in the elecber of bars of graphitesuperimposed upon' each other as shown in Fig. 7, by the horizontallines which cross the inclined apertures in the aphite sheets at theoint marked p, provided that the several bars are in close contact andare erforated' with inclined holes p or with e ges beveled as shown inFi 7, above and below 1) so as to allow the so ution to pass through thegraphite bars. On the side of the compound pervious electrodes E and Eis placed the cathode side 0 c of thecompound pervious electrode, whichmay be made of wire cloth, or fragments of an electro conductingsubstance whatever, bem always in electric contact with the ano e sideof the electrode of which it forms a part. The purpose of this form ofconstruction is to protect the anode side of the electrode from thecorrosive action of the electrolyte. Instead of graphite, latinum or inthe absence of chlorids and su fates, perforated sheet iron ma be used,but in all cases the aperture shou d be inclined in such a manner as toprotect the cathode side from the direct action of the oxidizingelectric current; while at the same time the solution is ableto passthrough the ervious cathode.

' Instead 0 using solid sheets or bars of graphite for the anode side ofthe compound pervious electrodes, the anode side maybe sufficient toprevent the electrical current y from oxidizing and dissolvin the metaldeposited upon the cathode si e of said compound pervious electrode. Athickness of granules of from 5 to 6 times the diameter of the grains ofcoke or graphite used is usually sufficient. I

It is seldom that this peculiar form of construction in Fig. 7 and itsequivalent here described, will be called for, but it is extremelyuseful in reducing the anode area below that of the cathode area whereit is desired to reduce the oxidizing effect on the solution. It isnecessar that the anode and cathode sides of each e ectrode be inelectrical contact either by direct contact with the anode plates orgranules or else by means of metalic or graphite rods suitablyconnecting the two sides of each electrode.

The advantages of compound pervious electrodes are very great when avery large number of electrodes are necessary in order to securecomplete deposition of the metallic content of the solution; for in thiscase we are required to have only two electric connections-the one bywhich'the posi tive current enters the deposition box, and the one bywhich it-leaves it. All the other electrodes are entirely withoutelectric connections. This relieves the operator from a great andendless source of trouble and annoyance, and simplifies theconstruction. Another advantage of this form of construction is thatshunt wound direct current dynamos, such as are ordinarily used forelectric lighting, may be used to advantage for the precipitation ofmetals, and a special .machine wound for quantity currents is no longernecessary. -Thus supposing one has at his disposition a shunt wounddirect current dynamo of 110 volts, and say, 10 amperes: supposing thatthe difference of potential between the successive electrodes which isfound necessary to give a good deposit'is 3 volts. In this case, besidesthe simple pervious anode by which the current enters the deposition boxB, and the simple pervious cathode by which it leaves the depositionbox, there are required 35 compound pervious electrodes, making in all.36 current gaps in the box each of which causing a tension of 3 volts,would make altogether 108 volts, which is about the capacity of themachine. When this installation is set up and operated, there passesthrough each electrodea current of 10 am peres, and each electrodereceives exactly the same amount of current. This form of construction,therefore, leads to very great simplicity in installation and facilityin management. While I prefer to place the electrodes vertically in saidbox, as shown in Fig. 6, for the reason that they are thus most easilyremoved and replaced, theymay be placed horizontally or in any otherposition. I do not claim to have discovered the advantages of compoundelectrodes in general, as suc electrodes made of solid imperviousmaterial have been used previously in electrometallurgy, but I do claimto ave discovered the fact that pervious electrodes may also act ascompound electrodes in great advantage.

the manner that I have described, with The material of which thesecompound pervious electrodes is made will depend u on and the meta to'berecovered. They may be made'of any pervious'material which is at once anelectric conductor, and is not too much acted .upon on the anode side bythe mous active surface for precipitation.

the solution to betreated' electrical conductor and is hardly acted uponat all by ordinary solutions even when acting as an anode. Thissubstance consists of small wire-like fragments of coke about the sizeof human hair, and it possesses an enor- But I do not confine myself toany one of the materials named, as any substance such as cloth madeconducting by being coated with some conducting substance, eithergraphite or some metallic film, may be used; but I refer the substancewhich is mentioned in the next paragraph.

My next improvement consists in a novel form of construction of perviouselectrodes, both simple pervious and compound pervious electrodes. Asatisfactory cathode for the recovery of metals from dilute solutionsmust be pervious must possess a maximum cathode surface in a minimumvolume; must be cheap; must be composed of material easily obtained inremote mining districts; must be little acted on by corrosive solutions;and must allow of easy recovery of the precipitated metals fr'om theelectrodes. All of these difficult conditions are for the first timeadmirably realized by my new form of ervious electrodes. This novel andimproved form of .pervious electrodes consists of a box with twopervious'sides inclosing a pervious mass of either fragmental, orpreferably filamental charcoal made electro-conducting by suitablemeans, as will be more fully described in what/follows.

Common commercial charcoal as ordinarily produced is practicallynonconduct ing, but by very simple means 1t may be rendered asufliciently good conductor to enable it-to be used as an electrode forthe deposition of metals. There are numerous methods by which this maybe accomplished,- thus if the charcoal is impregnated with some metallicsalt, such as a salt of gold, silver, copper, or other metal easilyreduced by the chemical action of the charcoal itself, as in the case ofchlorid of gold, or by heating the charcoal after impregnation with saidsalt as is the case with most metallic salts, or by the action of otherchemical agents such as sulfurous acid, sulfohydric acid or an alkalinesulfid or by heating the same to a red heat only, so that there isdeposited on thesurface of the charcoal a film, either of the metalitself, or of some conducting compound of the metal, such as sulfid. ofcopper or sullid of silver; the charcoal so-trcated then becomes asulliciently good conductor to act as an electrode. I have experimentedwith nitrate of silver, double cyanid of silver and potassium, chloridof gold, double cyanid of gold and potassium, sulfate of copper and many.other metallic salts. these forms may be used, but all have thedisadvantage of requiring the addition of some metallic substance to thecharcoal, which in many cases, has to be removed after treatment.

A second and much simpler method, which I much prefer, is to heat thecharcoal, preferably duringits manufacture, to a temperature of either ayellowish or white heat. A yellow heat is ordinarily suflicient. I havealso found that it becomes a better conductor if the charcoal is charredunder pressure, and

that the addition of small amounts of such substances as rosin,asphalt-um, bitumen, and other hydrocarbons, "during the charriIparticularly under pressure, tends to 1112 kc the charcoal a betterconductor so that as a cathode for the continuous deposition ofgold/silver, copper and other metals. I am well aware that charcoal hasbeen used for preci itating gold from solutions of chlorid of go d, andalso from cyanid solutions without the use of an electric current. Inthis case it acts chemically, and the amount of metal it willprecipitate is very lirrited, being ordinarily not more than one-fourthor at most a ound to a hundred pounds of the charcoal rom gold cyanidsolutions and eight pounds from chlorid of gold per hundred poundscharcoal.

When used as a cathode, as I shall explain later, the charcoal is simplyused as a conducting substance upon which indefinite quantities of gold,silver, copper and other metals may be recipitated so long as thecurrent flows. have thus been able to recipitate at a rate such thatupon a hun red pounds of charcoal, several hundred pounds of metal wouldbe de osited; there being no limit to the amount t at can beprecipitated in my method, exce t the convenience of the operator. Now,w ile charcoal, thus made an electric conductor by suitable means, maybe used in any pervious form whatever either fragmental'or filamental, Iprefer to arrange the pervious electrodes either simple perviouselectrodes-as described in the preceding section and shown in Figs. 1,2, and 3or compound pervious electrodesas described in Figs. 4, 5 and 6.Either form may be used as may be most convenient. In or- Any of der tosecure the maximum precipitating surface in the minimum volume for suchpervious electrodes I prefer to use the charcoal in a filamental form.For this purpose I prefer. to use charcoal, made from some fibrousorganic material such as ordinary cotton; the leaves of pine trees,common] called pine needles; or the fiber from the husks of cocoanuts;or hemp grass, or straw, or any other fibrous material of organicnature. As a rule, however, I find that cotton charcoal is usually sofine that it somewhat impedes the passage of the solution through it,and that it requires a very high tem erature to render it an electricconductor. l ine needles make a very good pervious charcoal, but theyhave the serious disadvantage of holding a large amount of ash,amounting to from 20 to 30 per cent. of their weight. ,The most suitablematerial that I have found for the purpose is charcoal made from thesubstance commonly used for packing freight, called Excelsior, amaterial usually made from soft pine Wood in the form of long shavingsnot more than one-sixteenth of an inch in width, and much less inthickness. 'The charcoal made from this material, when prepared as Ihave described, is an excellent conductor of electricity and possesses avery small amount of ash, not usually more than two or three per cent.of its welght. Charcoal made from common saw dust may also be used, butit is less ervious and hence not usually so well fitted or the purposeas that made from excelsior.

As charcoal is ordinaril prepared it is not an electric conductorancannot be used as an electrode, but when repared by any of the methodsdescribed above, it works in a thoroughly satisfactory manner. ever, itmust be an electric conductor to be of As, howany service, it isimportant that each lot of good conductor. An even simpler way istoimmerse the poles of an electric battery having a tension of about 4 or5fvolts into a bunch of the filaments. Ifwhen the circuit is made andbroken by touching the charcoal at different points withone of thewires, the other being in contact with it, a small spark appears whenthe current is made and broken, it is a sign that the same i'sa sufflciently good conductor for actual use. Or-

dlnary commercial charcoal does not respondto these tests unless itshould have been accidentally overheated when manufactured;

' they, are to be placed is not shown in these.

figures.

figures .have the same, significance.

As already stated, the charcoal filaments so prepared may be used eitheras simple pervious electrodes or as compound pervious electrodes, as maybe most convenlent. For this purpose I prefer to construct theelectrodes as shown in Figs. 8, 9, and 10. Fig 8 shows one of thesepervious electrodes. Fig. 9 is a vertical cross-section through three ofthese pervious electrodes. Fig. 10 is a view of threeof these. erviouselectrodes looked at from above. T e deposition box in which The lettersin all three of these Each 0 thepervious electrodes is preferably madein the form of a wooden box with two pervious sides. The box is made intwo parts designated by the letters F and F in' each case. The sides ofthe box across the direction of the circulation are made preferabl ofordinary cheese-cloth K. This cheese-c oth is stretched tight as a drumin the process of manufacture and is laced on one side of both parts ofthe box ike a sheet of glass in a window frame. Outside of thischeese-cloth frame is placed a wooden frame g, made either aboutone-eighth or one-fourth of an inch thick, to separate the cheese-clothpartitions of adjacent frames from each other. If the frame is madelarge enough to allow the cheese-cloth to bulge when filled withcharcoal, thus bringing about a short-circuit between the electrodes,the cheese-cloth is stiffened at intervals of from 4 to 6 inches by 1means of strips of wood, f and f like the division sashes of a windowframe, for the pur ose of reventing short-circuits. In sma il electro esthe thickness of these strips f and f and g need not exceed one-eighthof For large frames it would be safer to make them one-fourth of an incheach in thickness. The cheese-cloth may also be stiffened by ribs placedin the interior of the .box, provided the electric continuity of thecharcoal is not destroyed. Each electrode box is made of two parts whichfit together, making a single box. These parts are F p and F They arefastened at the bottom by suitable pins (marked 8) made preferably ofWoodor in some equivalent manner. At

.the top they may be fastened together by hooks H.

The'part marked F instead of being made -to contain charcoal, may bemade to act simly as a pervious lid to the other part of the box, Fcontaining charcoal. In this case the frame F is made preferably aboutinch deep with the cheese-cloth stretched ou the inner side. 1 The twoarts F and F are thus fastened together in t e same manner as that shownin Figs. 8, 9 and 10. This form of electrode is easier to fill andenipty than .the other forms, articularly when the lid is placed on thecatliode side of the compound pervious electrode boxes; for the metal isthen deposited just under the lid where it is easilyremoved.

In chargi the boxes ready. for use they are filled Wit filamentalcharcoal Q made electro conducting by any one of the methods reviouslydescribed. When ex celsior cliarcoal is used, I prefer to place in eachcubic foot of interior s ace about 2 or 4 pounds of the charcoal f1aments. When this is done there is left about 90 to 95 per cent. of voidspace through which the solution may'circulate, and which becomes filledwith gold, silver, copper, or other metal which is being precipitated.It is necessary to remember that the pervious charcoal is very brittle,hence it is important that it should be placed in the box with the leastamount'of reakage and that the cheese-cloth should be sufliciently fineto prevent the loss of small particles of anything but the finest dustfrom the charcoal. Each part of the box is care fully filled so as tomake a depth of charcoal, preferably about half an inch, and in such amanner as to be perfectly uniform in all parts and to a height above theline of the sloution in the deposition box. .Aftcr filling each half ofthe box in the manner described, the two parts of the box are assembledand fastened together by the pegs at the bottom and the hooks at thetop, or by other suitable means. After filling and assembling the twoparts, the packing should be close enough when held up to the light toprevent the light from penetrating any part of the compound perviouselectrodes; In order to prevent the electric current from leaking alongthe bottom and edges of the frames, I place a thin wooden diaphragm d ofwood or cloth soaked in paraffin paint in such a manner as to preventthe leakage of the electric current through the box without passingthrough the charcoal. It should project into the interior of the'boxabout one-fourth inch. Instead of this diaphragm, a tongue of wood maybe left on the inner edge of either or both half frames, or instead, theedges of the cheesecloth for about inch on the anode side may be aintedwith thick paraffin paint.

11 case the boxes are to serve as simple pervious electrodes, each onehas inserted through the center of the box in a vertical position, aconnecting wire of iron or some other metal, or preferably a rod ofelectrographite, so as to make electrical connection wit the ,main linecarrying the negative current; and the several pervious electrodes thusproduced are laced between. suitable ervious anodes as shown in Fig. 1).en the said boxes are intended to serve as compound pervious electrodes(as in Fig. 6), only the first and the last of these boxes are connectedby means of these connecting rods (marked G and G in Figs. 8, 9 and 10).

Figs. 9 and 10 show the arrangement used in compound pervious electrodesof this ty e set up ready for use, excepting only that t e depositionbox and the solution are not shown. In Figs. 9 and 10, .is a simplepervious anode with the connecting electrode G which is connected withthe positive conductor. E is a com ound pervious electrode without anycon ucting rod, and as many others similar to E may be inserted to theright of it as may be desired. Finally the ositive current escapes tothe negative con uctor G through the simple pervious cathode E, thecurrent escaping finally through the conductor rod G If the electrodesused are simple pervious cathodes with pervious anodes placed betweenthe several pervious cathodes, (as shown in Fig. 1), the charcoal oneither side of the pervious electrodes next to the cheesecloth becomescoated with a film of the metal deposited, either gold, silver, copper,or mixtures of these metals as the case may be. In case the electrodesare arranged as compound pervious electrodes, as E in Figs. 9 and 10,the whole being arranged as in Fig. 6, only the cathode side of thecharcoal in each of the compound pervious electrodes becomes coated withthe metal precipitated, the other side being either not acted upon atall, or being slightly oxidized by the current. To reduce this oxidationto a minimum I refer to pack oxidized on the anode side in most cases.

the charcoal closer on theano e than on the cathode side.

Instead of using electro-conducting charcoal made by the methodspreviously described, I may of course fill these boxes with any otherpervious conducti meterial such as coke or fragments of gra ite. Alsothe material known as coke whiskers ma be used, and also graphite in afilamental orm made by igniting the filamental charcoal to an intenseWhite heat in the electric furnace. The coke whiskers and the filamentalgraphite are almost entirely unacted upon by the solution, but thecharcoal is very slow%y 11 order to prevent this, I may also fill theanode side of the compound pervious electrodes either with pervious grahite plates orwith filamental carbon in the form of coke whiskers orfilamental graphite (as shown in Fig. 7 and already described), thecathode side being filled with filamental charcoal' After the metal hasbeen precipitated in a sufficient amount upon. the filamental charcoalor graphite or coke, I may recover it by making said cathodes anodes ina suitable solution on the principle explained in my previous Americanpatents 643,096, Feb. 6, 1900 and 756,328, September 9, 1903, or, in thecase that filamental charcoal is used, I may recover the metals in avery simple manner 7 by simply burning the charcoal in a suitablefurnace and smelting the ashes with suitable fluxes and if necessarysuitable reducin agents. If the charcoal has become coate( with manytimes its own weight of the metal, the product may be compressed intobricks, and melted down in a reverberatory furnace. In these ways I havebeen able to recover gold, silver, and copper with great ease and ittleexpense.

In some cases it is necessary to use a largle number of simple perviousanodes and cat odes, compound pervious electrodes not being suitable,and in these cases it is necessary to use. a substance insoluble in thesolution for the anode which introduces the positive current. I havefound that graphite made in the electric furnace, either in the form ofperforated sheets or in the form of rods of graphite inserted into aconducting rod either of graphite or metal, and projecting from the samelike the teeth of a comb, is very satisfactory with all solutionsexcepting those which contain sulfates, as sulfates of copper, sodium,etc. But when sulfates are present in the solution, the sulfuric acidset free at the anode attacks the graphite rods and slowly disintegratesthem. In such cases it is necessary to use some other substance. This isthe case with sulfate of copper and also with cyanid solutionscontaining alkaline sulfates. In such cases it has been customary to usestrips or perforated sheets of lead coated with peroxid of lead. Thissystem gives excellent results with sulfate of copper and also withcyanid solutions containing alkaline sulfates, so long as the coating ofperoxid of lead on the surface of the plate remains intact; but thissubstance is of a rather brittle nature, and if the lead is.

bent or scratched in any manner, it nearly always scales off and exposesthe naked lead beneath the oxid coating. When this takes lace the anodedeteriorates very rapidly.

his is a particular difficulty in cyanid solu tions, as the lead becomescoated with dense white crusts of cyanid of lead to the destruction ofthe anode and the loss of cyanid. I have discovered a very effectivemeans for overcoming this difficulty. For this purpose I construct aframe made of wood and shown in Fi s. 11 and 127 Fig. 11 shows a sidesectionaI elevation across the anode. Fig. 12 shows a vertical sectionthrough the anode. The wooden frame is marked F. When the frames aremade large I prefer to strengthen them by the horizontal cross bars q. Ithen take strips. of lead wire L from one-eighth to one-fourth of aninch in thickness, and of cylindrical form-and stretch them up and downthrough suitable holes bored in the horizontal bars of the frame, atdistances apart of from one-half inch to one inch or more, so as tostretch the lead wires like the wires of a harp alternately up and downplacing them in a groove in the lower horizontal cross bar. Where thewires pass over the lead busbar at the top they are secured to saidbusbar,preferably by the process of lead-burning rather than soldering,although soldering may be used, if necessary. The endof the lead busbaris connected at w with a copper wire which connects thesame with themain busbar of conductor introducing the positive current. After theanodes are thus constructed, I prepare the lead wires in the followingmanner.

In order to get a clean metallic surface on the outside of the wiresfree from all insulating materials, I connect the wire with the negativepole of a suitable source of electrical. energy, making the lead wirescathodes for a short time in a solution of plumbate of soda. Any oxid orcarbonate or hydrate that may have been formed on the outside of thelead wires becomes thus reduced to the metallic state and an evensurface is produced on the outside of the Wire of filamental lead.Without waiting for the film to oxidize in any way, the electric currentis immediately reversed and the lead- Wires are made anodes in the samesolution and are kept there until a firm, adherent, dark chocolate browncolored coating or peroxid of lead forms over every portion of the wireexposed to the action of the current. When this coating is formed to asufficient thickness to protect every portionof the wire, the same isthen covered with a cylindrical film or tube of firmly adherent peroxidof lead. The anodes are then ready to be inserted into the bath ofcopper sulfate or cyanid of gold or silver or other solution to betreated, for the purpose of acting as pervious peroxidized lead anodes.These peroxid coated lead wires may also be replaced by solid rodsofilead peroxid similarly arranged in a suitable frame.

I do not claim to have discovered or invented pervious electrodes noreroxidized lead anodes, nor compound solid or impervious electrodes. But

What I do claim as new and desire to secure by Letters Patent is 1.Compound pervious electrodes, each consisting of a suitable mass ofpervious The bottoms of the lead wires are electro-conducting material,arranged to act as a cathode on one side and as an anode on the other,and contained in a suitable portable non-conducting frame with pervioussides; means for retaining said compound pervious electrodes at suitableintervals in the solution to be treated, between a suitable .anode and asuitable cathode, both preferably also pervious means for connecting, bysuitable metallic conductors, said anode with the positive and saidcathode with the negative pole of an external directcurrent electricgenerator of sufiicient voltage to force a direct electric current toass continuously in the same direction an in series through said anode,the several intervening compound pervious electrodes, the cathode, andthe intervening solution in which all are placed; andmeans for passingsaid electric current from said anode through the solutionv to eachintervening compound pervious electrode, through the same and theintervening solution to the next inter vening compound perviouselectrode, and so on finally to the cathode at the end of the series,without the use of metallic conductors, and in such a manner as to causethat face of each intervening compound perviouselectrode nearest theanode'to be negativel electrified, and that face nearest the cathodetobe positively electrified, and so that there is a continuous fall ofvoltage from the anode where the current enters the solution, to thecathode, where it leaves it, all substantially as described.

2. Compound pervious electrodes consisting of fragmental or filamentalcharcoal made electroconducting by suitable means; means for retainingthe same in a box of non-conducting-material provided with pervioussides through which the solution to be treated may circulate; and meansfor passing a direct electric current through said solution and charcoalin such a manner that one face of each of said perviouselectroconducting charcoal masses shall tively electrified while theother is positively electrified.

3. Compound pervious electrodes containing on the anode side somesuitable pervious electro conducting material insoluble in theelectrolyte, and on the cathode side some suitable perviouselectro-conducting substance in electric contact with the anode side.

4. Simple pervious electrodes, composed of fragmental or 'filamentalcharcoal, made electro-conducting by suitable means, contained insuitable portable non-conducting frames with pervious sides; and meansfor connecting said simple pervious electrodes to the positive andnegative poles of an external direct-current electric generator,-

be nega so as to continuously charge all external In witness whereof Ihave hereunto set parts of said pervious electrodes with either my hand.

positive or negative electricity, according as they are to serve asanodes or cathodes, all SAMUEL B. CHRISTY.

.-- substantially as described.

5. Simplepervious anodes made of wires Witnesses: presenting a peroxidof lead surface, stretched J. COMPTON, upon suitable wooden frames. D.B. RICHARDS.

